Adaptive feedback method for cellular communication

• US 7,693,100 B2
• Filed: 04/20/2006
• Issued: 04/06/2010
• Est. Priority Date: 04/20/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd., Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Samsung Electronics Co. Ltd., Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Tang, Taiwen, Heath, Robert W., Cho, Sung-Hyun, Yun, Sang-Boh
• Primary Examiner(s): Patel; Ajit
• Assistant Examiner(s): PHAM, TIMOTHY X
• Application Number:
  US11/407,748
• Publication Number:
  US 20060256805A1
• Time in Patent Office: 1,447 Days
• Field of Search: 370/328, 370/431, 370/445
• US Class Current: 370/328
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0645 Variable feedback
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 72/1268 of uplink data flows

Abstract

In an adaptive feedback method for a cellular communication system having plural terminals feeding back channel information to an access point, the system selects one of an opportunistic mode and a polling mode as a feedback mode between an access point and the terminals on the basis of system and traffic parameters, sets up the access point and the terminals for the selected feedback mode, and feeds back the channel information from the terminals to the access point in the selected feedback mode. The adaptive feedback method changes the feedback mechanism adaptively to the system and traffic environment, making it possible to increase the system throughput as well as to decrease the MAC overhead regardless of the variation of the number of MSs.

Claims

1. An adaptive feedback method for a cellular communication system having a plurality of Mobile Stations (MSs) feeding back channel information to a Base Station (BS), comprising:

selecting one of an opportunistic mode and a polling mode as a feedback mode between the BS and the plurality of MSs on the basis of system and traffic parameters;

setting the BS and the plurality of MSs for the selected feedback mode; and

feeding back the channel information from the plurality of MSs to the BS in the selected feedback mode,

wherein the traffic parameters include a number ‘

N’

of active MSs from among the plurality of MSs and the system parameters include a number of mini-slots ‘

K’

carrying the channel information, and

wherein the step of selecting the feedback mode includes;

collecting the system and traffic parameters;

computing a mode selection parameter from the system and traffic parameters;

comparing the mode selection parameter with a predetermined threshold; and

selecting the opportunistic mode if the mode selection parameter is greater than or equal to the threshold; and

selecting the polling mode, if the mode selection parameter is less than the threshold.

2. The method of claim 1, wherein the mode selecting parameter is obtained by Q=N−

α

K, where α

is a tradeoff parameter for determining a switching point between the feedback modes.

3. The method of claim 2, wherein the threshold is ‘

0.’

4. The method of claim 1, wherein the step of setting the BS and the plurality of MSs includes:

optimizing control parameters associated with the selected feedback mode.

5. The method of claim 4, wherein the control parameters includes a channel power threshold η

and a random feedback probability p.

6. The method of claim 5, wherein the step of optimizing the control parameters for the opportunistic mode includes:

calculating a mean sum rate of all the plurality of MSs; and

determining the channel power threshold η and

the random feedback probability p to maximize the mean sum rate.

7. The method of claim 6, wherein the mean sum rate is calculated according to:

$C<br><br>\left(p,\mathrm{\eta <br><br>}\right)=\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>E_{\left({\mathrm{\chi <br><br>}}_j,S_j,T\right)}<br><br>\left[{\log }_2<br><br>\left(1+\mathrm{\rho <br><br>}<br><br><br><br>{\mathrm{\chi <br><br>}}_j\right)<br><br>I<br><br>\left\{S_j=1\right\}\right]$

where χ

_j is the channel power of a j^th MS, denoted by χ

_j=|h_j|² S_j is an event that the j^th MS is selected at the BS, T is the number of the plurality of MSs whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{•

} is an indicator function.

8. The method of claim 7, wherein the channel power threshold η

and the feedback probability p are determined according to;

max_p,η

C(p,η

)

s.t. 0≦

p≦

1, η

≧

0.

9. The method of claim 5, wherein the step of feeding back the channel information includes:

determining, at each of the plurality of MSs, whether a channel gain of the each of the plurality of MSs is greater than the channel power threshold η

; and

feeding back the channel information with the feedback probability p when the channel gain of the each of the plurality of MSs is greater than the channel power threshold η

.

10. A Base Station (BS) of a cellular communication system including a plurality of BSs, comprising:

a scheduler which schedules services for a plurality of Mobile Stations (MSs) and decides a service rate on the basis of channel information and traffic information with the respect to the services; and

a central feedback controller which generates feedback control signals for controlling a selected feedback mode,

wherein the BS operates in one of at least two feedback modes selected on the basis of a mode selection parameter and the plurality of MSs feed back channel information according to the selected feedback mode,

wherein the mode selection parameter is selected on the basis of a number ‘

N’

of active MSs from among the plurality of MSs and a number of mini-slots ‘

K’

carrying the channel information, and

wherein the central feedback controller includes;

a mode selector which selects the feedback mode by comparing the mode selection parameter with a threshold; and

an optimizer for optimizing the feedback mode selected by the mode selector and control parameters.

11. The BS of claim 10, wherein the mode selection parameter is calculated according to Q=N−

α

K, where Q is the selection parameter, N is the number of the plurality of the MSs, K is the number of minislots, and α

is a tradeoff parameter for deciding a mode switching point.

12. The BS of claim 11, wherein the control parameters includes a channel power threshold η

and a random feedback probability p.

13. The BS of claim 12, wherein the optimizer optimizes the selected feedback mode for maximizing system throughput.

14. The BS of claim 13, wherein the system throughput is a mean sum rate of the plurality of MSs.

15. The BS of claim 14, wherein the optimizer selects the channel power threshold and the random feedback probability maximizing the mean sum rate as optimal control parameters.

16. The BS of claim 15, wherein the mean sum rate is calculated according to:

$C<br><br>\left(p,\mathrm{\eta <br><br>}\right)=\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>E_{\left({\mathrm{\chi <br><br>}}_j,S_j,T\right)}<br><br>\left[{\log }_2<br><br>\left(1+\mathrm{\rho <br><br>}<br><br><br><br>{\mathrm{\chi <br><br>}}_j\right)<br><br>I<br><br>\left\{S_j=1\right\}\right]$

where χ

_j is the channel power of a j^th MS, denoted by χ

_j=|h_j|², S_j is an event that the j^th MS is selected at the BS, T is the number of the plurality of MSs whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{•

} is an indicator function.

17. The BS of claim 16, wherein the channel power threshold η

and the feedback probability p are determined according to;

max_p,η

C(p,η

)

s.t. 0≦

p≦

1, η

≧

0.